The present invention relates to techniques for transmitting packets in acknowledged mode from a master control unit to a slave terminal.
The invention relates more particularly, among these techniques, to those in which the control unit, which produces a sequence of blocks each comprising a header in addition to the user data, uses a “polling” mechanism to request acknowledgement of packets from the remote terminal. The header of each block then comprises an acknowledgement control field activated intermittently by the control unit so as to request acknowledgement of blocks from the terminal. In response to such a request, the terminal returns a message in which a certain number of previous blocks are acknowledged, positively and/or negatively.
A technique of this kind is used, in particular, for the downlinks (from the network to the mobile terminals) in GPRS (“General Packet Radio Service”) networks that have been developed to allow the transmission of data in packet mode in GSM (“Global System for Mobile communications”) type cellular networks.
The mechanism for acknowledging the packets may be disturbed when a block whose header has an activated acknowledgement control field is poorly received by the slave terminal. In this case, the terminal does not execute the acknowledgement request, so that the control unit remains uncertain as to the blocks that have been correctly received.
Often, the acknowledgement mechanism is used within the framework of an automatic repeat protocol (ARQ, “Automatic Repeat reQuest”) in which the unit sending the packets uses a send window of specified length, positioned onward of the first block which has not yet been positively acknowledged. If an acknowledgement request message has not been correctly received by the remote terminal, the send window may remain blocked at an old position, thereby leading to unnecessary repetitions of already received packets and to significant delays in the transmission of the new packets.
An object of the present invention is to propose an efficient method for transmitting data in packet mode.
Another object is to reduce the risks of blocking of the send windows utilized in certain ARQ mechanisms.